Ferroelectric random access memories (FeRAMs), which allows ferroelectric capacitors to retain information by utilizing polarization inversion of ferroelectric substances, are developed in recent years. A ferroelectric memory is a nonvolatile memory which does not lose retained information even when being powered off, and is particularly drawing attentions because of its ability to achieve high integration, high-speed drive, high durability, low power consumption, and so forth.
A ferroelectric oxide having a perovskite crystal structure with a large residual polarization amount, such as PZT (Pb(Zr,Ti)O3) or SBT (SrBi2Ta2O9), is mainly used as a material of a capacitor dielectric film constituting a ferroelectric capacitor.
Such a ferroelectric oxide is easily reduced by a reducing substance such as water or hydrogen and its ferroelectric characteristics such as residual polarization amount are thereby deteriorated. Accordingly, how to protect a capacitor against a reducing substance is an important factor in manufacturing a ferroelectric memory.
A protection insulating film for blocking water and the like is formed as the uppermost layer of a ferroelectric memory. The protection insulating film also has a role to protect the ferroelectric memory against a rays and mechanical impacts. Usually, a polyimide film is formed as the protection insulating film.
However, a polyimide film discharges water when being cured and cross-linked. Accordingly, there is a problem in the polyimide film that a ferroelectric capacitor is apt to be deteriorated by water. Moreover, a substrate needs to be heated to a relatively high temperature of 250° C. to 350° C. for achieving complete cross-linking of polyimide, and the ferroelectric capacitor is apt to be damaged by the heat as well.
Although polyimide is commonly used as a protection insulating film for typical types of memories including a DRAM (dynamic random access memory) and a flash memory, a new film to replace the polyimide film is required as a protection insulating film for a ferroelectric memory in order to prevent the above problems.
As a protection insulating film which replaces the polyimide film, a novolac resin film is proposed in Japanese Laid-open Patent Publication No. 2005-62764. As disclosed in Japanese Laid-open Patent Publication No. 2003-29297 and Japanese Patent No. 2567685, a novolac resin is a material originally used as a main component of a photoresist. According to Japanese Laid-open Patent Publication No. 2005-62764, a protection insulating film excellent in coating and adhesion properties is obtained by adding an amide-acid polymer to an alkali-soluble phenol novolac resin or an alkali-soluble cresol novolac resin.
Note that techniques related to the present application are also disclosed in Japanese Laid-open Patent Publication No. 2005-62764, Japanese Laid-open Patent Publication No. 2003-29297, Japanese Patent No. 2567685, International Publication Pamphlet No. WO 01/020650, Japanese Laid-open Patent Publication No. 2002-343708, Japanese Laid-open Patent Publication No. 2006-5223, and Japanese Patent No. 3654597.